Do authors have a "duty to warn"?

A couple of weeks ago the very first novel I ever wrote, Funerals for Horses, got a scathing 1–star review on Amazon from a person who said “someone should have warned” her that there was sex in the book. Well, I did, actually, in my new introduction. I didn’t respond, of course, because I don’t think authors should ever respond to reviews. But I did begin to discuss it a bit on Facebook in the context of a recent post regarding authors leaving reviewers alone.

Interestingly, I heard from another woman, a Facebook friend, who also strongly believes in book “warnings.” She feels that if a book contains sex it should say so in the promotional description, because otherwise she will already have spent her money by the time she finds out, and it will be too late.

Actually, the book is for sale exclusively on Amazon, and the reader can use the “look inside” feature before buying. Plus Amazon ebooks can be returned for a full refund in the first few days.

That said, I’m looking further into whether something should be said in the book description of Funerals for Horses. But I have a feeling the problem will not be so easily solved. While I totally support people’s right to read only what they care to read, I’m not sure the author can solve the problem with warnings.

Here's where I stand on "warning" readers. Or, at least, where I think I stand. I’m hoping to hear from readers and get more information that will help me decide.

How do I know where the reader’s line will fall regarding sex? I have a couple of books in which characters have sex, but it's described in very non-specific, emotional-observations-only terms. Do they need a warning? What about the adult edition of Pay It Forward? Reuben and Arlene have sex, but we leave them at the bedroom door. But they wake up in the same bed. Does that need a warning?

I'm really shocked by how many people won't read a book with "swearing" in it. Do I need to warn about that? What about damn and hell? Does that count? If I soften the s-word by saying "crap," will that offend? Some people it will, other people it won’t.

I’ve actually had readers write to me to learn in advance if the name of God is taken in vain in one of my books. I did a search for one person, and found that it was used in sentences like, “I hope to God it’s okay,” but not in the context of swearing. I returned that information, saying I hoped it helped. The reader in question said it did, but without telling me where it fell on his line. But it wouldn’t have changed much if he had, because someone else’s line will be different.

I myself don't like to read books with upsettingly detailed violence. But how can the people who market the book know how much violence I will find upsetting?

Then there are people who will not read a book in which an animal is mistreated, or even one in which a pet dies a natural death.

Several people complained about When I Found You, feeling that they should have known in advance that the book includes boxing and hunting, because those are activities they don’t like.

I’m really not saying any of this sarcastically, or as if my view is the only one. I just don’t know how an author can  address in advance what a reader might find unacceptable. I may still decide to warn about the sex issue in Funerals for Horses, if only because it’s so different from my newer books, and I can understand why some readers would have come to expect something different from me. But I wonder if the only real solution to the problem at hand is for the reader to read the free sample, then buy the book, then stop reading and return the book if they feel they’ve made a mistake.

I’ve been in the book business for a long time, and this feels like a new problem to me. I never heard a word about a responsibility to warn readers about sex and language until a year or two ago. I’d be interested in hearing what my readers think on the subject. Because if I should be doing better to help readers have a good experience with my work, I want to know.